The development of an in vivo system permitting the "at will" control of virogene marker expression by the manipulation of the host's endocrine milieu now provides a model to comprehensively examine the relevance of virus information in tumorigenesis. Efforts will be concentrated on physiological imbalances as they interact with host genetics and immunocompetence in the induction and propagation of the malignant state. Furthermore, attempts will be directed toward the characterization of the underlying biochemical mechanisms of these interrelationships.